A gas and steam turbine installation with integrated gasification of fossil fuel usually includes a gasification device for the fuel, which on the outlet side is connected to the combustion chamber of the gas turbine via a number of components provided for gas purification purposes. A heat recovery steam generator, the heating surfaces of which are connected into the water steam circuit of a steam turbine, may be connected downstream of the gas turbine on the flue gas side. An installation of this type is known, for example, from GB A 2 234 984 or U.S. Pat. No. 4,697,415.
To reduce the emission of pollutants during the combustion of the gasified fossil fuel or synthesis gas, a saturator, in which the synthesis gas is laden with steam when the installation is operating, may be connected into the gas line. For this purpose, the gasified fuel flows through the saturator in countercurrent to a flow of water which is passed through a water circuit referred to as the saturator circuit. To achieve a particularly high level of efficiency, there is provision for heat from the water steam circuit of a gas and steam turbine installation to be introduced into the saturator circuit.
As a result of contact with the heated flow of water guided in the saturator circuit in the saturator, the gasified fuel is saturated with steam and is heated to a limited extent. For thermal reasons and also for operating reasons, it may be necessary to further heat the fuel before it is fed into the combustion chamber of the gas turbine.
DE 19 832 293 A1 has described a gas and steam turbine installation having a heat recovery steam generator connected downstream of the gas turbine on the flue gas side. The heating surfaces of the heat recovery steam generator are in this case connected into the water steam circuit of the steam turbine. A gasification device for fuel is connected upstream of the combustion chamber, via a fuel line, for the purpose of integrated gasification of a fossil fuel for the combustion chamber. To achieve a particularly high efficiency in the installation, the fuel line, between the gasification device and the saturator, includes, in addition to a mixing device for admixing nitrogen, a heat exchanger on the primary side, which on the secondary side is likewise connected into the fuel line, between the saturator and the combustion chamber.
A similar gas and steam turbine installation to that described in DE 19 832 293 A1 is disclosed by WO 00/20728. It is intended for it to be possible for the gas and steam turbine installation described in that document to be operated with a particularly high level of efficiency even when oil is used as fossil fuel.
For this purpose, in WO/20728, a heat exchanger is connected into the fuel line on the primary side, upstream of a mixing device for admixing nitrogen to the gasified fuel, as seen in the direction of flow of the gasified fuel, which heat exchanger, on the secondary side, is designed as an evaporator for a flow medium. On the steam side, the heat exchanger is connected to the combustion chamber of the gas turbine.
To ensure particularly reliable operation of the gas and steam turbine installation, it should be possible for a feed of the synthesis gas into the combustion chamber of the gas turbine to be stopped at any time. For this purpose, a quick closing fitting should usually be connected into the gas line upstream of the combustion chamber. When required, the quick closing fitting blocks off the gas line within a particularly short time, so that it is impossible for any synthesis gas to enter the combustion chamber assigned to the gas turbine.
On account of the relevant safety regulations, the fuel system usually includes a gas lock. A gas lock includes two fittings, for example ball valves, which can be opened or closed to a flow of gas. An intermediate relief or a pressure line is connected in between these two fittings. The intermediate relief may be connected to an excess gas burner, via which excess gas can be burnt off. As an alternative to the intermediate relief, the pressure line can be connected up, ensuring that it is impossible for any gas to flow in via the gas lock fittings. The gas lock therefore separates the fuel system in gastight manner in a first region or the gasification system upstream of the gas lock and in a second region or what is known as the gas turbine fuel system downstream of the gas lock.
A gas and steam turbine installation with gasification device can be operated both with the synthesis gas, which is generated, for example, from coal, industrial residues or garbage, and with a second fuel, such as for example natural gas or oil. In the event of a changeover from synthesis gas to second fuel or vice versa, it is for safety reasons necessary for the region between the gas lock and the combustion chamber, i.e. the gas turbine fuel system, to be purged with an inert medium, such as nitrogen or steam.
To allow a gas and steam turbine installation to be optionally operated with the synthesis gas from a gasification device or a second or substitute fuel, the burner in the combustion chamber assigned to the gas turbine has to be designed as a two fuel or multi fuel burner, to which both the synthesis gas and the second fuel, e.g. natural gas or fuel oil, can be fed according to the particular requirements. The corresponding fuel is in this case supplied to the combustion zone via a fuel passage in the burner.